1. Field of the Invention
The present invention relates to a method for heat treatment of a glass substrate suitable for the production of a display panel such as a plasma display panel or a liquid crystal display panel.
2. Prior Art
The production of a plasma display panel (hereinafter referred to as PDP) includes a step for laminating or forming a laminate such as an electrode material, a dielectric material, a diaphragm or a fluorescent material on a glass substrate by means of screen printing or photolithographic technique. In such a forming step, it is usually necessary to heat-treat each laminate at a temperature of from 500.degree. to 600.degree. C. in order to dry and sinter the material laminated on the substrate. Namely, the substrate will be subjected to heating and cooling repeatedly.
It is generally known that glass undergoes a change in the specific volume by heat treatment. Due to such a dimensional change of glass, deviation of the laminated material from the pattern is likely to result, the operation efficiency for bonding the front substrate and the rear substrate tends to deteriorate, or a cross talk is likely to take place in the display.
Heretofore, in order to suppress extension or shrinkage of glass during such heat treatment, it has been common to use a glass having high strain point, or to stabilize extension or shrinkage of glass by pre-heat treatment i.e. by preliminarily heat treating the glass in a pattern close to the temperature conditions for heat treatment. However, even when a glass having a high strain point is used, such extensibility or shrinkage of glass can not completely be removed. The pre-heat treatment is effective to some extent when the heat treatment step is only once during the production of a panel, but when heat treatment is repeated a plurality of times, it is difficult to suppress extension or shrinkage of glass in the second and subsequent heat treatments, since the degree of extensibility or shrinkage differs in every heat treatment.
On the other hand, in recent years, along with the progress in sophistication of picture elements of a display, an improvement in precision of a film-forming technique is required, and an improvement of dimensional stability during heat treatment of glass has been increasingly important.
The present invention is intended to solve the above-mentioned problems of the prior art and to present a technical means to control extensibility and shrinkage of glass during heat treatment of a glass substrate.